1. Field of the Invention
The present invention relates to a high-strength aluminum alloy having good porthole extrudability.
2. Description of the Prior Art
Aluminum and aluminum alloys, when used as an extrusion material, can easily provide sections having a complicated profile, leading to the widespread use thereof in various fields such as building materials. Among such aluminum alloys, high-strength aluminum alloys, by virtue of high specific strength, have become widely utilized in various fields. Conventional high-strength aluminum alloys of the above type known in the art include JIS 2000 series (Al--Cu-base alloys), JIS 5000 series (Al--Mg-base alloys), and JIS 7000 series (Al--Zn--Mg-base alloys).
Hollow materials, such as extruded aluminum pipes, have hitherto been produced by porthole extrusion using a porthole die. In porthole extrusion, aluminum is divided in a port section of the porthole die into a plurality of portions which are again joined (welded) to each other in a chamber section to form a welded portion, thereby preparing a hollow section having a complicated profile.
However, it should be noted that although, for example, the production of components required to have abrasion resistance, such as rollers for copying machines, requires the use of abrasion-resistant aluminum alloys, such as JIS 4000 series alloys, it is impossible to conduct porthole extrusion of the JIS 4000 series alloys. In order to eliminate such a problem, Japanese Unexamined Patent Publication (Kokai) No. 4-176835 discloses an aluminum alloy containing boron.
Even in the case of porthole extrusion using this aluminum alloy, unsatisfactory welding occurs when aluminum is divided in a port section of the porthole die into a plurality of portions which are again joined to each other in a chamber section to form a welded portion. For this reason, no sound hollow sections can be provided, and, hence, only a solid section having no welded portion or a mandrel pipe can be produced and the production of hollow sections having a complicated profile is difficult.
Further, in the case of, for example, an Al--Mg-base alloy, when the Mg content exceeds 2% by weight, the welded portion in the section formed using this alloy is reported to have lowered strength and toughness. In fact, the production of hollow sections using JIS alloys 5052, 5056, and 5083 and the like by porthole extrusion is impossible, and hollow sections having a complicated profile cannot be produced by extrusion. Thus, the conventional high-strength aluminum alloys cannot be used for the production of hollow sections having a complicated profile, and, hence, the scope of applications thereof is limited.